The present invention relates generally to apparatus and methods for controlling and guiding a continuous web of flexible material (e.g., plastic film, fabric, paper, etc.) as the web is advanced along a path of conveyance, and relates more particularly to apparatus and methods for controlling the positioning of an edge of an advancing web relative to a device performing an operation along the edge. In particular embodiments, the invention relates to apparatus and methods for controlling and guiding an inflatable web.
In the processing of continuous webs of material, there is often a need to perform an operation on the web along one longitudinal edge of the web, wherein the positioning of the edge relative to the device performing the operation can be important or even critical to the quality and/or the success of the operation. For example, it may be desirable to form a feature (e.g., a seal, a line of stitching, a perforation, etc.) in the web along the edge, and to accurately control the position of such feature relative to the edge. In such contexts, it is desirable to accurately control the transverse positioning of the edge of the web relative to the device.
In the particular application of manufacture of gas-inflated products such as cushions for packaging or the like, in some cases the cushions are formed from a web having two plies of plastic film that are sealed together in a pattern defining inflatable chambers that are in communication with a channel or opening along one longitudinal edge of the web. The web is advanced from its supply roll to an inflation device that has a portion extending between the two plies along the longitudinal edge for inflating the chambers. The plies are then sealed together using a sealing device so as to seal the chambers closed. The transverse positioning of the edge of the web relative to the inflation and sealing devices can be important to the quality and/or success of the inflation and sealing operations.
Various approaches have been employed for controlling the edge position of such an inflatable web. As one example, U.S. patent application Ser. No. 11/181,136 filed on Jul. 14, 2005, the entire disclosure of which is incorporated herein by reference, describes an edge position control system that includes a tracking sensor used to detect the transverse position of the web with respect to the inflation device. A web tracking system is employed to continually adjust the transverse position of the web to maintain it within a predetermined range with respect to the inflation device. In this manner, the consistency of inflation of the inflatable chambers is improved.
The present invention, in particular embodiments directed to inflatable webs, represents a further development of edge position control apparatus and methods for web inflation machines, and furthermore is more generally applicable to other types of web-handling systems and methods wherein it is desired to control the edge positioning of a web.